This invention relates to a process for producing silver-ionic water (or silver ion-containing water) used in the field of, for example, sanitary administration in processing, distribution and selling of foods, soil conditioning and cultivation promortion in agriculture, environmental sanitation in medical care, etc., and an apparatus for producing the same.
Silver-ionic water, which is less dangerous for human bodies and has an bactericidal action, has recently attracted notices as potable water, sterilized water and so forth.
In the present invention, the actions expected in silver ions include a bacteriostatic action against bacteria, an action of supplying activie oxygen to roots of plants, an action of supplying OH ions for the purpose of promoting photosynthesis in the cells of plants with a lower amount of light, and actions such as elimination of pains, hemostasis and promotion of a vulnerary action. Of these, the bacteriostatic action originates from the oxidation catalytic function inherent in silver acting on a cell membrane of bacteria, the silver concentration, and the pH of ionic water. Upon contact of silver ions with a bacterial body, the catalytic function of silver may cause a radical reaction in the unsaturated aliphatic acid constituting a hydrophobic part of a cell membrane of bacteria to hydrolyze the same. The cell membrane of bacteria thereby loses its function, aiming at stopping vital activities by inflow of water, and DNA and constitutents of a nuclear membrane may not be affected by the catalytic function of silver to remain in a sound form. Moreover, silver tends to be little accumulated inside a living body as compared with other metallic elements. From these facts, silver ions are considered to be little dangerous for human bodies and, from a genetic viewpoint also, cause no disorder in a fetus that may affect a next generation, and therefore, if conditions are adjusted, has a possibility to serve as a new bacteriostatic agent substituting conventional chemical medicaments.
Conventionally, the silver-ionic water has been produced by an apparatus embodying a process called a Katadyn process. This apparatus comprises an anode and a cathode, wherein the anode is provided with silver, and water is allowed to pass while a voltage is applied between both electrodes, whereby silver is ionized and dissolved out to give silver-ionic water.
However, the apparatus mentioned above is involved in a problem that the resulting silver-ionic water is substantially neutral, and, under the neutral condition, silver ions may be adsorbed on proteins and can have only a little chance for direct contact with the inside of a cell of a bacterial body when proteins are contained in water or bacteria are in contact with proteins, resulting in an extreme lowering of its bacteriostatic action. Specifically speaking based on an experimental work made by the present inventors, this silver-ionic water was brought into contact with bacteria in an aqueous solution in which proteins are dissolved, and also, separately, with bacteria adhered to proteins, but, because of the neutral environment, metallic ions were vigorously bonded to proteins, releasing ions, and was not able to enter the cells of bacteria when brought into contact with the bacteria, with the loss of the effect by silver ions and no achievement of the object.
To cope with the problem, the present inventors have made intensive studies. As a result, they have found that silver-ionic water having a given silver ion concentration under the acidic condition of pH 5 or less or the alkaline condition of pH 8 or more may have a remarkable bacteriostatic action against bacteria present together with proteins, with a silver ion concentration that may be less dangerous for human bodies, and that the acidic silver-ionic water has an action of supplying O.sub.2 to roots of plants and the alkaline silver-ionic water, when supplied to plant cells, has an action of promoting photosynthesis.
As an apparatus for producing acidic or alkaline silver-ionic water, known is an apparatus as disclosed in Japanese Unexamined Patent Publication No. 97088/1985, for example. As shown in FIG. 3, this apparatus comprises an electrolytic cell 11 provided with an anode 12 comprising a silver electrode, and a cathode 13 comprising a carbon electrode or the like, wherein a cylindrical ion-exchange diaphragm 14 is disposed around the anode 12, which diaphragm 14 defines an anode compartment 15 and a cathode compartment 16 which are separated from each other. Water passes through branch pipes 17a and 17b of a conduit 17, and is led into the anode compartment 15 and the cathode compartment 16, respectively. One end of a feedback pipe 18 is connected to the bottom of the cathode compartment 16, and the other end of the feedback pipe 18 opens to an upper portion of the anode compartment 15. Water in the cathode compartment 15 circulates to the anode compartment 15 through the feedback pipe 18. Also, a take-out pipe 19 is connected to the bottom fo the anode compartment 15 and another take-out pipe 20 is connected to the bottom of the cathode compartment 16.
Thus, in this prior art apparatus, water is introduced into the anode compartment 15 and the cathode compartment 16 through the branch pipes 17a and 17b of the conduit 17, and allowed to circulate from the cathode compartment 16 to the anode compartment 15 trough the feedback pipe 18. Further, the water in the anode compartment 15 is taken out from the take-out pipe 19 and the water in the cathode compartment 16 is taken out from the take-out pipe 20. By applying a direct-current voltage to the anode 12 and the cathode 13, silver on the anode 12 is ionized to dissolve. Acidic silver-ionic water is taken out from the take-out pipe 19 of the anode compartment 15 and alkaline silver-ionic water is taken out from the take-out pipe 20 of the cathode compartment 16. Here, since the water in the cathode compartment 16 is allowed to circulate to the anode compartment 15 through the feedback pipe 18, the water taken out from the anode compartment 16 and the cathode compartment 16 may have substantially the same silver ion concentration.
However, in the above apparatus, a high voltage have had to be applied in order to attain the desired EC value by applying a voltage to the anode 12 and the cathode 13. Therefore, because of the silver electrode provided on the anode 12, if it is attempted to increase the silver ion concentration of the water to be taken out, silver particles beings to precipitate to form colloids when the silver ion concentration reaches a certain level. Thus, there has been a limit in increasing the silver ion concentration. Moreover, there has been a fear of adversely affecting human bodies when a large quantity of silver grains are precipitated to form colloids.